The present invention relates to a gas exchange valve drive for a valve-controlled combustion engine. In particular, the invention relates to a gas exchange valve where the reciprocating movement of the valve member is not effected and controlled by a cam shaft. Rather, the valve member is electrically actuated by the inventive gas exchange valve.
From DE 195 18 056 A1 a gas valve control with a gas exchange valve is known, which is actuated by an electromagnet arrangement. By means of a special configuration of the pole shaft of the electromagnet arrangement, a signal related to the movement of the armature is generated in the control line of the electromagnet arrangement. This signal can be evaluated for detecting any armature position without additional sensors. A considerable problem with the employment of an electromagnet arrangement for operating the valve is the high noise level developing upon reaching the respective end positions, the abrupt braking upon reaching the end positions, as well as the required high holding currents.
The same applies to differential electromagnet arrangements which have been proposed on several occasions, which are specifically subjected to an increasing current for achieving the required thrust of approx. 300-400 N for combustion engines of passenger cars. Therein, the valve which is biased by a spring arrangement initially performs an oscillating movement before an iron plate arranged at the valve shaft abuts the armature of the electromagnet arrangement so that a much lower holding current is required. Here, the maximum speed of the engine, however, is considerably limited. The start-up time upon starting is relatively long because of the required high force it takes some time for the valve arrangement to oscillate into its desired position.
From JP-A-3-92518 a drive means for a valve arrangement in combustion engines is known, wherein the stator is built from two approximately semi-cylindrical shells which comprise teeth, split both in the circumferential direction and in the longitudinal direction of each shell, facing towards the rotor. The individual teeth of each shell are each surrounded by a coil the center longitudinal axis of which extends in the radial direction. This results in a magnetic flux oriented in the radial direction, which originating from each of the plurality of teeth flows through the air gap between stator and rotor into the rotor.
An insofar corresponding configuration of the stator, the stator coils, and the rotor of a drive means for a valve arrangement in combustion engines is described in U.S. Pat. No. 5,129,369. In this case, too, teeth of the stator, which are split in the radial and tangential direction, are surrounded by a coil each whose_ center longitudinal axis extends in the radial direction.
EP 0 485 231 A1, too, shows a similar type of the stator design, the stator coils, and the rotor of a drive means for a valve arrangement in combustion engines. In this case, too, teeth of the stator, which are split in the radial and tangential direction, are surrounded by a radially oriented coil each.
These arrangements necessitate a very high manufacturing expenditure because the assembly of the coils around the individual teeth is difficult to realize. Moreover, the pole pitch which can be achieved with this construction is relatively large.
From WO98/55741 a valve arrangement for a valve-controlled combustion engine is known, with an electric travelling-field motor as an actuator for a valve member, which comprises a rotor coupled with a valve member and a stator. The stator is built from plates whose surfaces are oriented vertically to the direction of movement of the rotor. The stator has teeth facing towards the rotor which is designed as a synchronous or asynchronous rotor, each of which having a closed lateral cylinder area facing towards the rotor. Between two neighbouring teeth each of the stator, stator coil chambers are formed in which a coil each is arranged with is oriented parallel to the area of the plates.
From U.S. Pat. No. 6,039,014 a valve arrangement driven by a linear motor for a combustion engine is known. Here, the stator of the linear motor comprises several coils which are separated from each other by a ferromagnetic housing section each. A rotor is built from several sections of a permanent-magnetic material, between which sections are arranged, each consisting of a ferromagnetic material.
Further documents which show the technical background for the invention include, without claiming to be exhaustive: DE 33 07 070 A1; DE 35 00 530 A1; EP 244 878 B1; WO90/07635; U.S. Pat. No. 4,829,947; EP 377 244 B1; EP 347 211 B1; EP 390 519 B1; EP 328 194 B1; EP 377 251 B1; EP 312 216 B1; U.S. Pat. Nos. 4,967,702; U.S. Pat. No. 3,853,102; U.S. Pat. No. 4,829,947; U.S. Pat. No. 4,915,015; WO90/07637, WO90/07637; EP 328 195 A2.
All concepts which are described in the above mentioned documents have in common that they are unable to achieve the stroke, thrust, and dynamics required for gas exchange valves in combustion engines with adequate compact construction and high reliability for large series application in automotive engines. Moreover, known arrangements are manufactured in a very space consuming and expensive manner. Finally, these arrangement are also not suited for the application in high-speed (fast-running) combustion engines, because none of these arrangements is optimized with respect to the moved masses.
For the elimination of these drawbacks, the invention teaches a gas exchange valve drive for a valve-controlled combustion engine with a linear motor as the actuator for a valve member, which is defined by the characteristics of Claim 1.
According to the invention the gas exchange valve drive for a valve-controlled combustion engine has a hollow cylindrical rotor to be coupled with a valve member, and a stator, with the rotor comprising permanent-magnetic rings arranged concentrically above each other, the stator being at least partially formed from a soft magnetic material and comprising at least one tooth facing towards the rotor, the stator comprising a radially inner magnetically conductive area and a radially outer magnetically conductive area, with the rings of the rotor being arranged between the inner area and the outer area of the stator, and the outer area of the stator having a C-shaped cross-sectional configuration in the radial direction in at least one partial section and comprising at least one stator coil.
The concept on which the invention is based consists in spatially xe2x80x9cremovingxe2x80x9d the portion of the stator which effects the armature magnetomotive force, i.e. the coil area with the stator coil, from the portion generating the force of the linear motor, i.e. the tooth area of the stator. Compared to conventional linear motors where the stator coils are arranged between two teeth each of the stator, a considerably higher magnetomotive force of the armature can be achieved. This is dues to the fact that the coil is subjected to considerably less spatial restrictions due to the inventive design and can therefore to optimized to minimal (ohmic) losses- and the associated maximal magnetic field induction. By the dimensions of the permanent-magnetic rings in the direction, of movement of the rotor or the dimensions of a tooth of the stator in the direction of movement of the rotor, respectively, a pole pitch is defined which is smaller than the dimension of the stator coil in its longitudinal direction.
Simultaneously, the rotor magnetic pole/stator tooth arrangements generating force or movement, respectively, are concentrated so that these are not interrupted by stator coils. This allows a very small pole pitch which in turn effects a high force density. In addition, the inventive arrangement allows partial strokes of the valve member. Thus, it is possible with a combustion engine equipped with the inventive gas exchange valve drives to dispense with a throttle valve for metering the air/fuel mixture and its associated control.
By the inventive design magnetic flux is induced in the C-shaped yokes of the outer area of the stator by the stator coil(s) arranged there, which flows from the radial sections of the C-shaped yokes via the annular air gap in which the hollow cylindrical permanent magnets are arranged into the inner (cylindrically shaped) area of the stator. From the inner area of the stator, the magnetic circuit is closed again towards the C-shaped yokes of the outer area of the stator.
A further essential advantage of the inventive gas exchange valve drive is that virtually only the magnetically effective components (the permanent magnets) contribute to the inert mass of the rotor, while all other parts of the motor (coils, magnetic yoke, etc.) are associated with the stator. This makes it possible to achieve a particularly high ratio between the force exerted by the motor and inert mass. Moreover, the inventive gas exchange valve drive is excellently suited to be employed in high-speed combustion engines. This allows in particular the approach of the valve member to the end positions (open or closed position of the gas exchange valve) at high speed with high changes in acceleration, so that the valve member contacts the valve seat at minimum speed, while the valve member is otherwise moved at very high speeds. Moreover, the maximum force is available in the end areas of the course of movement. This allows a very low-noise and low-wear operation of the inventive gas exchange valves, which is simultaneously very reliable due to the attainable high holding forces in the end positions.
Due to the fact that several single-phase motors connected in series which can be controlled individually can be provided in the inventive gas exchange valve drive, the total generated force along the stroke travel of the valve member can be adjusted exactly to the force required in the respective instance. In this context it should be noted that the inventive gas exchange valve drive is generally to be operated in a single-phase manner. It is, however, also possible to operate the stator coils of the individual motors arranged one above the other in a multi-phase manner. Due to the inventive arrangement it is not necessary to subject the valve member with a considerable kinetic energy in order to have it assume its end position.
Due to the arrangement of the stator coil(s) which can be formed very simple (single-phase and cylindrical) it is possible to keep the vibratory forces low acting on the coil so that vibrations of the coil or friction of the coil against the wall of the stator coil chamber are low. Thus it is possible to do with a minimum amount of insulating material or liner material, respectively, of the stator coil chamber. This also contributes to the compactness and reliability of the overall arrangement. In addition, this causes a high power density even with small gas exchange valves, because the space filling factor (coil volume in the stator coil chamber related to the total volume of the stator coil chamber) is high.
Compared to the known (e.g. from U.S. Pat. No. 6,039,014) arrangements, the inventive arrangement minimizes the leakage fluxes and allows a very efficient assembly of several gas exchange valves arranged adjacent to one another, with neighboring gas exchange valve drives being able to at least partially alternately utilize the magnetic yoke. This enables the minimization of mass and volume of the magnetic yoke body.
The coil area in the direction of movement of the rotor is preferably larger than the distance between two neighboring teeth of the stator.
The stator can be formed in a known manner from electric sheet steel parts. For a simplified manufacture it is, however, also possible to form it, at least partially, from a soft magnetic form body, preferably from pressed and/or sintered metal powder. Preferably, the stator comprises a strip-wound coil from soft magnetic sheet metal strip, with a soft magnetic form body, each, preferably from pressed and/or sintered metal powder, being arranged at the faces for forming the teeth. In order to increase the saturation inductance of the stator it is also advantageous that the soft magnetic forming body of the stator comprises at least one core with cobalt-containing iron in its interior, which is preferably formed as a sheet metal wound coil.
In a preferred embodiment, the stator is assigned a displacement sensor for detecting the stroke of the valve member. This can, for example, be an interferometer or an inductive sensor with a carrier frequency. This is advantageous in particular, because also partial strokes (i.e. intermediate positions between open and closed) of the valve arrangement are possible with the inventive actuator. This partial stroke can be sensed or controlled, respectively, via the sensor.
The rotor is at least partially surrounded by a magnetic yoke body of the stator. The coil of the stator can then be arranged either at the stator or in the magnetic yoke body.
The magnetically alternately oriented permanent magnet rings can additionally be maintained at a predetermined distance from one another by magnetically not effective spacers from a light material (aluminum, titanium, synthetic materialxe2x80x94also with glass or carbon fiber reinforcement or the like). Thus, the inert mass of the rotor can be kept small.
According to the invention the stator is constructed from a soft magnetic material and has teeth facing towards the rotor. Between two neighboring teeth of the stator a winding chamber can be formed in which a winding is arranged. The rotor comprises rings from permanent-magnetic material. These magnet rings are concentrically arranged one above the other and their magnetic orientation is designed in such a manner that in a predetermined position of the rotor two teeth each of the stator are in alignment with a magnet ring with the opposite magnetic orientation.
For forming an external rotor motor the stator is at least partially surrounded by the rotorxe2x80x94separated by an air gap. In a similar manner, the rotor is at least partially surrounded by the stator for forming an internal rotor motor. According to the invention it is also possible to form the stator by permanent magnet disks arranged above each other, while the rotor comprises a winding chamber which is defined by corresponding soft magnetic annular disks.
The high force density which can be realized with the inventive embodiments can be achieved among other things by dimensioning the teeth or the permanent magnets, respectively, which are located opposite them relative to the axial extension of the winding chamber sufficiently short so that there is space available for at least two further permanent magnets (each with a different magnetic orientation).
According to the invention, the rotor of a preferred embodiment is at least partially surrounded by a magnetic yoke body. In particular in the case of the employment of several gas exchange valves arranged side by side, it is advantageous to provide at least two winding chamber with teeth, windings in the stator and corresponding permanent magnets in the rotor at each gas exchange valve, with the winding in the neighboring gas exchange valve being controlled in an opposite sense in such a manner that the magnetic fluxes through the magnetic yoke body comprise as little leakage flux proportions through the magnetic yoke body as possible. Thus the volumexe2x80x94and the weightxe2x80x94of the magnetic yoke body can be kept small. Moreover, the power losses are minimized thereby. An essential aspect is that the magnetic yoke body comprises the shape of a section tube with an approximately rectangular cross-section, with two opposite walls being provided with break-outs through which the inner part of the stator (coil arrangements) and the rotor protrude. This arrangement minimizes the leakage flues and allows, in particular, a very efficient assembly of several such gas exchange valves arranged side by side, whereinxe2x80x94under the provision of a corresponding electric control neighboring gas exchange valve drives can at least partially alternately utilize the magnetic yoke. This enable the minimization of mass (and volume) of the magnetic yoke body.
Finally, the invention relates to an engine with internal combustion with at least one combustion cylinder with at least one valve arrangement for inlet or outlet valves with one or several of the above characteristics.
From the inventive design of the gas exchange valve drive the following properties result:
High dynamics with low power consumption.
A spring arrangement for the compensation of the forces generated by moved masses is not required to realize an end position change (from open to closed or vice versa) of the valve member in less than 1.5 ms at an average power consumption over two complete crankshaft rotations of less than approx. 100 W with a mass of the valve member of approx. 30-70 g, a valve stroke of approx. 5-10 mm, and a speed of a 4-cylinder combustion engine of at least 6000 rpm. 10 mm, and a speed of a 4-cylinder combustion engine of at least 6000 rpm.
In the respective end positions of the valve member, only low holding currents are required for reliably holding the valve member in the respective position.
Due to the fact that a spring arrangement is dispensed with (see above), the otherwise necessary oscillatory action of the valve member is omitted. This reduces the duration of the setting operation.
By means of the inventive actuator, the valve member can precisely be brought into any desired position from virtually each current position. This applies in particular to the end positions which can very precisely be approached by the valve member. It is thus possiblexe2x80x94by means of a corresponding electronic control of the coil(s)xe2x80x94to ensure an impact of the valve member on its valve seat with less than 40 mm/s. This keeps wear and noise generation of the valve arrangement during operation at a very low level.
The valve memberxe2x80x94though rigidly connected with the rotorxe2x80x94may be supported rotatably with respect to its valve seat about its axis of movement so that punctual wear of the valve member or the valve seat is avoided.
Due to the high power density of the inventive arrangement the transverse dimensions (diameters) of the gas exchange valve with the required specifications can be kept very small. This allows the employment in compact passenger car engines.
Further characteristics, properties, advantages, and possible modifications will be explained with reference to the following description in which the accompanying drawings are referred to.